Process for developing an electrophotographic printing material

ABSTRACT

A process is described for developing an electrophotographic printing material, said process being capable of improving the printed image of the electrophotographic printing material by treating the photoconductive layer of the printing material with a surface-treating solution prepared by dissolving a two- or multi- component copolymer in paraffinic hydrocarbon, said copolymer containing at least one monomer selected from each of the following first and second group of monomers, the first group of monomers having an oleophilic group and the second group of monomers having a basic nitrogen atom.

nited States Patent lkeda et a].

[451 Mar. 21, 1972 [54] PROCESS FOR DEVELOPING AN ELECTROPHOTOGRAPHIC PRINTING MATERIAL [72] Inventors: Itsuo Ikeda; Nobuyuki Katagiri, both of Tokyo, Japan [73] Assignee: Kabushiki Kaisha Ricoh, Tokyo, Japan [22] Filed: June 10, 1969 [21] Appl.No.: 831,933

[30] Foreign Application Priority Data June 15, 1968 Japan ..43/41228 [52] U.S. Cl. ..96/1 LY, 117/37 LE, 252/62.l

[51] Int. Cl. ..G03g 13/00 [58] Field ofSearch ..96/1, 1 LX, 1.5; 117/37 LX [56] References Cited UNITED STATES PATENTS 3,512,965 5/1970 Matkan ..96/1

FORElGN PATENTS OR APPLICATIONS 1,509,571 l/l968 France ..96/]

Primary Examiner-George F. Lesmes Assistant Examiner-John R. Miller Attorney-Burgess, Ryan & Hicks [5 7] ABSTRACT 3 Claims, 1 Drawing Figure Patented March 21, 1972- F ECTION DENSITY o 2+ @QMW REL Y i 2' i AMOUNT OF EXPOSURE logEt INVENTORS [TSUO Mao/a N050 yum KA TA G/R/ aura A44 ATTORNEYS PROCESS FOR DEVELOPING AN ELECTROPIIOTOGRA'PHIC PRINTING MATERIAL BACKGROUND OF THE DISCLOSURE A. Field of the Invention The invention relates to a process for developing an electrophotographic printing material, comprising treating the photoconductive layer of the printing material with a specific surface-treating solution before or after carrying out the development of the printing material in a liquid developer.

B. Description of the Prior Art The developing processes in a liquid developer of the electrophotographic printing material consist in that an electrostatic latent image is produced by irnage-wise exposure of a developer and toners of the developer are precipitated according to the charge on the photoconductive layer, to form a visible printed image. For the purpose of improving the density and contrast of the printed image, there has been proposed a means of controlling the particle size of the toner. But, the toner having a small particle size is attracted by very low electrostatic charge to be precipitated on the nonimage area and to give a fog, and accordingly a vivid printed image having a good contrast can not be obtained. On the contrary, the toner having a large particle size is difficult to be attracted by electrostatic charge, and accordingly the printed image having a high density can not be obtained.

It is, therefore, an object of this invention to provide a process for developing an electrophotographic printing material capable of giving a printed image having a high density and good contrast.

SUMMARY OF THE INVENTION The present invention relates to a process for developing an electrophotographic printing material and, more particularly, to a process capable of improving the printed image of the printing material by treating the photoconductive layer of the printing material with a specific surface-treating solution before or after carrying out the development of the printing material in a liquid developer.

The present invention is based on the principle that certain surfactants or specific copolymers are selectively adsorbed on the unexposed area of the photoconductive layer of the electrophotographic printing material. To prevent that, the toner of the liquid developer is attracted to said unexposed area, and is removed from the unexposed area.

According to the present invention, an excellent (vivid and clear) printed image may be obtained on the electrophotographic printing material.

It has been found that an excellent printed image may be obtained by treating the printing material with a surface-treating solution before or after carrying out the development of the printing material in a liquid developer. The surface-treating solution comprises a surfactant dissolved in an organic solvent, said surfactant being a specific copolymer which is selectively adsorbed on the unexposed area of the photoconductive layer of the printing material and not adsorbed on the exposed area thereof. The organic solvent is a paraffinic hydrocarbon which has a high resistivity (more than (t-cm.) and a low dielectric constant (less than 3).

The specific copolymer contains at least one monomer selected from each of the following first and second group of monomers:

the first group of monomers (monomers having oleophilic group) include,

a. a vinyl higher alkyl ether,

b. a lower alkyl ester of an unsaturated acid such as acrylic acid, methacrylic acid or fumaric acid,

c. a lower alkylstyrene,

the second group of monomers (monomers having basic nitrogen atom), include a. vinylpyridine,

b. aminostyrene,

photoconductive layer, which image is developed by a liquid c. an amino lower-alkyl ester of an unsaturated acid such as acrylic acid, methacrylic acid or'fumaric acid,

d. an-acid amide of an unsaturated acid such as acrylic acid,

methacrylic acid or fumaric acid.

The aforementioned paraffinic hydrocarbon-is, for example, Isopar H (trademark; made by Esso-Standard Oil Co.) or Shellsol trademark; made by Shell Oil-Co.

The electrophotographic material which can be used in this invention, includes any conventional electrophotographic printing material, said printing material being one containing in the photoconductive layer any substances capable of producing potential difference between'the unexposed and exposed areas when irradiated with ultraviolet ray, visible ray, infraredray or radiation and said substances being photoconductive substance such as zinc oxide, cadmium sulfide, lead sulfide or selenium; semiconductors such as germanium or silicon and an organic semiconductor, which must be stable in the liquid carrier-of the developer.

The liquid developer which can be used in this invention, includes any of the conventional liquid developers; a liquid developer which has been prepared by dispersing a mixture of pigment (e.g., carbon black having particle size of about 'rp) and the aforementioned specific copolymer in the aforementioned parafiinic hydrocarbon (liquid carrier), may be advantageously used. The toner of this liquid developer has a negative charge in the liquid carrier; this liquid developer is of the negative-positive type.

This invention is available for two types of processes for developing electrophotographic printing material (1) a printing material which is subjected to imagewise exposure to light and then development in a liquid developer, and (2) printing material which is charged by coronadischarge and subjected to imagewise exposure to light and "then bias-development in a liquid development. The bias-development will be shown in the example set out below.

DESCRIPTION OF THE DRAWING The appended drawing shows characteristic curves representing the relation between the amount of exposure (Et) and the density of the printed image (D). The exposure (Et) is the product of [wt (Lx) in lumens/m. and time(s) in seconds, while the density (D) is measured by densitometric methods.

These curves are obtained by over-laying an image original having various (ten-odd) image densities on the printing material, followed by exposure to light and then subjected to development in a liquid developer.

The curves 1 and 2 are those obtained by means of the chargeless development, and the curves 3 and 4 are those obtained by the bias-development.

The curves 1 and 3 are those obtained by the process of this invention, and the curves 2 and 4 are those obtained by the conventional process for the purpose of comparison.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is further illustrated by the following nonlimitative examples.

EXAMPLE 1 photoconductive zinc oxide (made by Sakai Chemical Industry Co., Ltd) styrenated alkyd resin (trademark "Styresol No. 4250"; made by Dainippon Ink and Chemicals Inc.)

toluene lOOg,

IOOg.

vinyldecyl ether-vinyldiethylaminoethyl ether copolymer lsopar H 0.1g. lOOg.

The printing material thus treated was developed in a liquid developer of the negative-positive type which has been prepared by dispersing the following ingredients in 100g. of lsopar H by means of ultrasonic disperser and said printing material gave a very vivid printed image without fogging.

carbon black 0.2 (trademark "Mogul A"; made by Godfley L, Cabot Inc.)

vinyldecyl ether-vinyldiethylaminoethyl ether copolymer 0.2g.

EXAMPLE 2 The same procedure as described in Example 1 was repeated except that the treatment of the printing material by the surface-treating solution was carried out after the printed image has been formed by developing. A vivid printed image similar to that of Example 1 was obtained.

EXAMPLE 3 A surface-treating solution was prepared from the following ingredients:

octadecyl methacrylate-4- 0.05g. vinylpyridine copolymer Shellsol T 100g.

A liquid developer was prepared by mixing the following ingredients in a ball mill and by dispersing 5g. of the mixture thus obtained in lOOg. of kerosene.

carbon lack (trademark Mitsubishi Color Carbon No. 44"; made by Mitsubishi Chemical Co.)

alkyd resin (trademark "Rhodene L/IOO; made by Polymer Corp. Interstate Proprietary Ltd.)

alkyd resin modified by phenol (trademark Pentapol made by Polymer Corp. Interstate Proprietary Ltd.)

kerosene The particle size of the toner in this liquid developer was about 0. l.

The same procedures described in Examples 1 and 2 were repeated with the above prepared surface-treating solution and liquid developer, and vivid printed images similar to those of Examples 1 and 2 were obtained.

EXAMPLE 4 A surface-treating solution was prepared from the following ingredients:

dodecyl methacrylate-vinyldiethyl- 0.1g. aminoethyl ether copolymer lsopar H lOOg.

The procedures of Examples 1, 2 and 3 were repeated except that the above prepared surface-treating solution was used as a substitute for those of Examples 1 and 3. Vivid printed images similar to those of Examples 1, 2 and 3 were obtained.

EXAMPLE 5 A surface-treating solution was prepared from the following ingredients:

vinyldecyl elher-vinyldiethyl- 0.0lg. aminoethyl ether copolymer lsopar H l00gv The same procedure as that of Example 1 was repeated except that the electrophotographic printing material was charged by corona discharge of 5.5kv. at intervals of 1.5cm. before said material was image-wisely exposed to a 500w. tungsten lamp; the above prepared surface-treating solution was employed and material was subjected to bias-development in the liquid developer.

The bias-development was carried out as follows: after the printing material was exposed to the lamp, it was dipped into the liquid developer in the metallic vessel and an electrode was placed over the material at intervals of 3mm. The DC voltage of 3.5V, was applied to the electrode and the metallic vessel, the electrode being cathode and the vessel being anode.

The printed image thus obtained was very vivid.

Referring to the appended drawing, the image density (A) thus obtained was compared with the image density (B) obtained without using the aforementioned surface-treating solution and the image density (C) obtained with using only lsopar H for the surface-treating solution. The results were as follows:

Reflection density ofthe printed Reflection density of the nonimage image area A (curve 3) L35 0.16 B (curve 4) 1.35 0.50 C L35 0.45

EXAMPLE 6 The same procedure as described in Example 5 was repeated except that, after the bias-development was carried out, the printing material was dipped in the surface-treating solution. Results similar to that set out in Example 5 was obtained.

EXAMPLE 7 A surface-treating solution was prepared from the following ingredients:

octadecyl methacrylate-4- 0.005 vinylpyridine copolymer Shellsol T lOOg.

The same procedures as that described in Examples 5 and 6 were repeated except that the above prepared surface-treatin g solution and the liquid developer which were prepared in Example 3 were used in the place of the surface-treating solution and the liquid developer of Example 5. Results similar to those of Examples 5 and 6 were obtained.

EXAMPLES 8 dodecyl methacrylate-vinyldiethyl- 0.0lgr aminoethyl ether copolymer lsopar H The same procedures described in Examples 5, 6 and 7 were repeated except that the above prepared surface-treating solution was employed in place of the surface-treating solution of Examples 5 and 7. Printed images similar to those of Examples 5, 6 and 7 were obtained.

We claim:

1. A process for developing an electrophotographic printing material comprising the steps of imagewise exposure to light and development in a liquid developer wherein the photoconductive layer of said printing material is treated with a surfacetreating solution after exposure and before or after development, said solution being prepared by dissolving a copolymer in a paraffinic hydrocarbon having a resistivity of more than 10 ().cm. and a dielectric constant of less than 3, said copolymer containing at least one monomer selected from each of the following first and second groups of monomers; the first group of monomers being members of the group consisting of a vinyl higher alkyl ether, a lower alkyl ester of an ethylenically unsaturated carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and fumaric acid, and a lower alkyl styrene, the second group of monomers being selected from the group consisting of vinylpyridine, aminostyrene, an amino lower alkyl ester of an unsaturated acid selected from the group consisting of acrylic acid, methacrylic acid and fumaric acid and an acid amide of an unsaturated acid selected from the group consisting of acrylic acid, methacrylic acid and fumaric acid.

2. The process as defined in claim 1 wherein the photoconductive layer of the printing material is treated with said surface-treating solution after exposure before carrying out the development of the printing material.

3. The process as defined in claim 1 wherein said printing material is treated with said surface-treating solution after carrying out the development of the printing material. 

2. The process as defined in claim 1 wherein the photoconductive layer of the printing material is treated with said surface-treating solution after exposure before carrying out the development of the printing material.
 3. The process as defined in claim 1 wherein said printing material is treated with said surface-treating solution after carrying out the development of the printing material. 